Adaptive predistortion system

US 6,252,912 B1
Filed: 12/24/1997
Issued: 06/26/2001
Est. Priority Date: 12/24/1997
Status: Expired due to Term

First Claim

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1. A method for adaptively compensating a digital signal, comprising the following steps:

accumulating statistical information at a receiver regarding a received signal transmitted by a transmitter, said accumulating step comprising the further steps of accumulating symbol cluster statistical information, accumulating weighted sums of the symbol coordinates to produce first, second and third matrices, inverting said first matrix and multiplying said inverted first matrix by said second matrix to produce a first coefficient matrix of the coefficients for a first coordinate of the constellation used in a least squares model for estimating the center of each symbol cluster, and multiplying said inverted first matrix by said third matrix to produce a second coefficient matrix of the coefficients for a second coordinate of the constellation used in said least squares model for estimating the center of each symbol cluster;

determining constellation distortions due to at least one voltage offset, gain mismatch ratio, lock angle error, quad angle error, nonlinear channel distortions and receiver distortions;

compensating for said constellation distortions in at least one of the in-phase and quadrature signal components of said signal;

processing said statistical information to determine compensation values; and

using said compensation values to compensate said signal.

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Abstract

A method and apparatus are described for adaptively predistorting a signal before it is transmitted by a transmitter in order to compensate for nonlinearities which are introduced. Statistical information regarding the received signal is accumulated at a receiver, and is preferably transmitted back to the transmitter for processing. The processing includes a constellation analysis to determine the distortion characteristics of the signal, which may include bias, gain imbalance, lock and quad angle errors, and nonlinear distortions including AM-AM and AM-PM conversion effects, with all of these phenomena occurring anywhere in the transmitter-channel-receiverchain. From analysis of the statistics of the distortions in the received signal constellation, adjustments are made in the transmitter and/or receiver parameters. The positions of the signal symbols in the transmitted constellation are thereby correctively predistorted to compensate for and ameliorate the distortions in the received signal, thereby improving the fidelity of the said received signal.

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54 Claims

1. A method for adaptively compensating a digital signal, comprising the following steps:
- accumulating statistical information at a receiver regarding a received signal transmitted by a transmitter, said accumulating step comprising the further steps of accumulating symbol cluster statistical information, accumulating weighted sums of the symbol coordinates to produce first, second and third matrices, inverting said first matrix and multiplying said inverted first matrix by said second matrix to produce a first coefficient matrix of the coefficients for a first coordinate of the constellation used in a least squares model for estimating the center of each symbol cluster, and multiplying said inverted first matrix by said third matrix to produce a second coefficient matrix of the coefficients for a second coordinate of the constellation used in said least squares model for estimating the center of each symbol cluster;
  
  determining constellation distortions due to at least one voltage offset, gain mismatch ratio, lock angle error, quad angle error, nonlinear channel distortions and receiver distortions;
  
  compensating for said constellation distortions in at least one of the in-phase and quadrature signal components of said signal;
  
  processing said statistical information to determine compensation values; and
  
  using said compensation values to compensate said signal.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
- - 2. The method of claim 1, wherein said digital signal includes at least one of QAM (quadrature amplitude modulation), TCM (trellis coded modulation), CAP (carrierless AM/PM), MPSK (multiple phase shift keying), QPR (quadrature partial response) and signal constellations.
  - 3. The method of claim 1, wherein said step of accumulating constellation statistical information and said processing step are used to determine predistortion parameters, said method comprising the further step of using said predistortion parameters to predistort said signal prior to transmission of said signal, whereby said received signal symbol clusters are properly located in accordance with predetermined signal decision boundaries.
  - 4. The method of claim 1, further comprising the following steps:
5. The method of claim 1, wherein said compensating step is performed at one of the transmitter and receiver.
6. The method of claim 1, further comprising the following steps:
- using a memory-based predistorter to compensate said signal;
  
  determining any residual nonlinear distortion still present in said signal; and
  
  if so, adaptively predistorting said signal to substantially eliminate said residual nonlinear distortion.
7. The method of claim 1, wherein control information indicative of said constellation distortions is exchanged between said transmitter and said receiver over a narrow bandwidth control channel.
8. The method of claim 7, wherein parameters in at least one of said receiver and transmitter are adjusted to correct distortions in said constellation arising from previously set parameter values.
9. The method of claim 1, wherein the step of determining constellation distortions due to lock angle error comprises the following steps:
- determining at least one of the magnitude and direction of the lock angle error in the constellation; and
  
  shifting the carrier phase in at least one of the transmitter and receiver to rotate the constellation in a direction and an amount which reduces the lock angle error.
10. The method of claim 1, wherein the step of determining constellation distortions due to quad angle error comprises the following steps:
- determining at least one of the magnitude and direction of the quad angle error; and
  
  adjusting at least one of the modulator quadrature phase shifter in the transmitter and the demodulator quadrature phase shifter in the receiver in a direction and an amount to reduce the quad angle error.
11. The method of claim 1, wherein the step of determining constellation distortions due to voltage offset comprises the following steps:
- determining the magnitude of the voltage offset; and
  
  adjusting the bias voltage in at least one of the transmitter and receiver in a direction and an amount to reduce the voltage offset.
12. The method of claim 1, wherein the step of determining constellation distortions due to gain mismatch ratio comprises the following steps:
- determining the magnitude of the gain mismatch ratio; and
  
  adjusting the amplifier gains in at least one of the transmitter and receiver in a direction and an amount to reduce the gain mismatch ratio.
13. The method of claim 1, wherein the step of determining constellation distortions due to nonlinear channel distortion comprises the following steps:
- determining the magnitude of the nonlinear channel distortion; and
  
  adjusting the position of each symbol within the constellation in at least one of the transmitter and receiver in a direction and an amount to reduce the nonlinear channel distortion.
14. The method of claim 1, wherein said first and second coordinates are the x and y cartesian coordinate dimensions of said symbol clusters, respectively.
15. The method of claim 1, wherein the step of accumulating weighted sums is performed in accordance with the following relationships to produce said first, second and third matrices, designated A, B_xand B_y:
- $A = \sum_{i = 1}^{M} \sum_{j = 1}^{M} \sum_{k = 1}^{K_{ij}} \langle \begin{matrix} 1 & l_{ik} & m_{jk} & l_{ik}^{2} & m_{jk}^{2} & l_{ik}^{3} & m_{jk}^{3} \\ l_{ik} & l_{ik}^{2} & l_{ik} m_{jk} & l_{ik}^{3} & l_{ik} m_{jk}^{2} & l_{ik}^{4} & l_{ik} m_{jk}^{3} \\ m_{jk} & l_{ik} m_{jk} & m_{jk}^{2} & l_{ik}^{2} m_{jk} & m_{jk}^{3} & l_{ik}^{3} m_{jk} & m_{jk}^{4} \\ l_{ik}^{2} & l_{ik}^{3} & l_{ik}^{2} m_{jk} & l_{ik}^{4} & l_{ik}^{2} m_{jk}^{2} & l_{ik}^{5} & l_{ik}^{2} m_{jk}^{3} \\ m_{jk}^{2} & l_{ik} m_{jk}^{2} & m_{jk}^{3} & l_{ik}^{2} m_{jk}^{2} & m_{jk}^{4} & l_{ik}^{3} m_{jk}^{2} & m_{jk}^{5} \\ l_{ik}^{3} & l_{ik}^{4} & l_{ik}^{3} m_{jk} & l_{ik}^{5} & l_{ik}^{3} m_{jk}^{2} & l_{ik}^{6} & l_{ik}^{3} m_{jk}^{3} \\ m_{jk}^{3} & l_{ik} m_{jk}^{3} & m_{jk}^{4} & l_{ik}^{2} m_{jk}^{3} & m_{jk}^{5} & l_{ik}^{3} m_{jk}^{3} & m_{jk}^{6} \end{matrix} \rangle, B_{x =} \sum_{i = 1}^{M} \sum_{j = 1}^{M} \sum_{k = 1}^{K_{ij}} \langle \begin{matrix} x_{ijk} \\ l_{ik} x_{ijk} \\ m_{jk} x_{ijk} \\ l_{ik}^{2} x_{ijk} \\ m_{jk}^{2} x_{ijk} \\ l_{ik}^{3} x_{ijk} \\ m_{jk}^{3} x_{ijk} \end{matrix} \rangle, B_{y} = \sum_{i = 1}^{M} \sum_{j = 1}^{M} \sum_{k = 1}^{K_{ij}} \langle \begin{matrix} y_{ijk} \\ l_{ik} y_{ijk} \\ m_{jk} y_{ijk} \\ l_{ik}^{2} y_{ijk} \\ m_{jk}^{2} y_{ijk} \\ l_{ik}^{3} y_{ijk} \\ m_{jk}^{3} y_{ijk} \end{matrix} \rangle .$ wherein 1 is defined as (i−
  
  (M+1)/2) and m is defined as (j−
  
  (M+1/2)), M is the number of symbols in each coordinate of the constellation and i and j are integers ranging from 1 to M which indicate the location of each cluster.
16. The method of claim 15, wherein said first and second coordinate coefficient matrices are of the form:
17. The method of claim 16, wherein said gain mismatch ratio R_Gis defined as the following ratio B_xx/B_yy.
18. The method of claim 16, wherein said second and third order gain mismatch ratios R_G2and R_G3are defined as the following ratios, respectively, C_xx/C_yyand D_xx/D_yy.
19. The method of claim 16, wherein said lock angle error is determined in accordance with the following relationship:
- $θ = \frac{1}{2} (\tan^{- 1} \frac{B_{xy}}{B_{yy}} - \tan^{- 1} \frac{B_{yx}}{B_{xx}}) .$
20. The method of claim 16, wherein said quad angle error is determined in accordance with the following relationship:
- $\begin{matrix} \begin{matrix} Ψ = ψ_{x} - ψ_{y} \\ = - \tan^{- 1} \frac{B_{yx}}{B_{xx}} - \tan^{- 1} \frac{B_{xy}}{B_{yy}} . \end{matrix} \end{matrix}$
21. The method of claim 16, wherein the coefficient parameters are used to define the following quantities:
- $S_{Q} = \sqrt{B_{yy}^{2} + B_{xy}^{2}}, D_{a} = \sqrt{B_{xx} + B_{xy}^{2} + B_{yy} + B_{yx}^{2}}, D_{b} = \sqrt{B_{xx} - B_{xy}^{2} + B_{yy} - B_{yx}^{2}} .$
22. The method of claim 21, wherein lock angle error is determined in accordance with the following relationship:
- $θ = \frac{1}{2} \cos^{- 1} [\frac{D_{a}^{2} + D_{b}^{2} - 4 S_{Q}^{2}}{2 D_{a} D_{b}}] - \tan^{- 1} (\frac{B_{yy} + B_{yx}}{B_{xx} + B_{xy}}) .$
23. The method of claim 21, wherein the gain mismatch ratio is determined in accordance with the following relationship:
- $R_{G} = \sqrt{\frac{4 S_{Q}^{2} - {(D_{a} - D_{b})}^{2}}{{(D_{a} + D_{b})}^{2} - 4 S_{Q}^{2}}} .$
24. The method of claims 1 or 16, wherein said method is performed in a repeater circuit.
25. The method of claim 1, wherein said processing step is performed at one of said transmitter and receiver.
26. The method of claim 1, wherein compensating step is performed at one of said transmitter and receiver.

27. A method for adaptively compensating a digital signal which is being transmitted by a transmitter and received by a receiver, comprising the following steps:
- modulating a digital signal at the transmitter according to a predetermined modulation scheme;
  
  adaptively compensating said modulated signal at said transmitter in accordance with compensation values determined from statistical information accumulated at the receiver regarding the received signal;
  
  transmitting said compensated modulated signal to said receiver;
  
  receiving said compensated modulated signal at said receiver;
  
  accumulating statistical information at said receiver regarding said received signal, said accumulating step comprising the further steps of accumulating symbol cluster statistical information and using said symbol cluster statistical information to accumulate constellation statistical information, accumulating weighted sums of the symbol coordinates to produce first, second and third matrices;
  
  inverting said first matrix and multiplying said inverted first matrix by said second matrix to produce a first coefficient matrix of the coefficients for a first coordinate of the constellation used in a least squares model for estimating the center of each symbol cluster;
  
  multiplying said inverted first matrix by said third matrix to produce a second coefficient matrix of the coefficients for a second coordinate of the constellation used in said least squares model for estimating the center of each symbol cluster;
  
  processing said statistical information to determine compensation values for constellation distortions due to at least one of voltage offset, gain mismatch ratio, lock angle error, quad angle error, nonlinear channel distortions and receiver distortions;
  
  wherein said adaptive compensation step compensates for said constellation distortions in at least one of the in-phase and quadrature signal components of said signal.
- View Dependent Claims (28, 29, 30, 31)
- - 28. The method of claim 27, wherein said receiver transmits said statistical information over a reverse control channel to said transmitter and said processing step is performed at said transmitter.
  - 29. The method of claim 27, wherein said processing step is performed at said receiver and said receiver transmits said compensation values to said transmitter over a reverse control channel.
  - 30. The method of claim 27, further comprising the step of compensating said modulated signals using a memory-based predistorter.
  - 31. The method of claim 27, wherein said digital signal is part of a signal constellation, and said method further comprises the steps of partitioning said signal constellation into a plurality of sub-constellations and performing said accumulating and processing steps for the signals within each sub-constellation.

32. A method for adaptively compensating a digital signal which is being transmitted by a transmitter and received by a receiver, comprising the following steps:
- modulating a digital signal at the transmitter according to a predetermined modulation scheme;
  
  adaptively compensating said modulated signal at said receiver in accordance with compensation values determined from statistical information accumulated at the receiver regarding the received signal;
  
  transmitting said modulated signal to said receiver;
  
  receiving said modulated signal at said receiver;
  
  accumulating statistical information at said receiver regarding said received signal, said accumulating step comprising the further steps of accumulating symbol cluster statistical information and using said symbol cluster statistical information to accumulate constellation statistical information, accumulating weighted sums of the symbol coordinates to produce first, second and third matrices;
  
  inverting said first matrix and multiplying said inverted first matrix by said second matrix to produce a first coefficient matrix of the coefficients for a first coordinate of the constellation used in a least squares model for estimating the center of each symbol cluster;
  
  multiplying said inverted first matrix by said third matrix to produce a second coefficient matrix of the coefficients for a second coordinate of the constellation used in said least squares model for estimating the center of each symbol cluster;
  
  processing said statistical information to determine compensation values for constellation distortions due to at least one of voltage offset, gain mismatch ratio, lock angle error, quad angle error, nonlinear channel distortions and receiver distortions;
  
  wherein said adaptive compensation step compensates for said constellation distortions in at least one of the in-phase and quadrature signal components of said signal.
- View Dependent Claims (33, 34, 35, 36)
- - 33. The method of claim 32, wherein said receiver transmits said statistical information over a reverse control channel to said transmitter, said processing step is performed at said transmitter and said transmitter transmits compensation values to said receiver over a forward control channel.
  - 34. The method of claim 32, wherein said processing step is performed at said receiver.
  - 35. The method of claim 32, further comprising the step of compensating said modulated signals using a memory-based predistorter.
  - 36. The method of claim 32, wherein said digital signal is part of a signal constellation, and said method further comprises the steps of partitioning said signal constellation into a plurality of sub-constellations and performing said accumulating and processing steps for the signals within each sub-constellation.

37. An adaptive compensation system for compensating a digital signal, comprising:
- a statistical accumulation circuit which accumulates statistical information at a receiver regarding a received signal transmitted by a transmitter, said accumulation involving the accumulation of a symbol cluster statistical information which is used to accumulate constellation statistical information;
  
  a compensation value determination circuit which processes said statistical information to determine compensation values; and
  
  a compensation circuit which uses said compensation values to compensate said signal;
  
  a constellation distortion estimation circuit which determines the constellation distortions due to at least one voltage offset, gain mismatch ratio, lock angle error, quad angle error, nonlinear channel distortions and receiver distortions;
  
  wherein said compensation circuit compensates for said constellation distortions in at least one of the in-phase quadrature signal components of said signal; and
  
  wherein said statistical accumulation circuit further comprises a weighted sum circuit which accumulates weighted sums of the symbol coordinates to produce first, second and third matrices, a matrix inversion circuit which inverts said first matrix and multiplies said inverted first matrix by said second matrix to produce a first coefficient matrix of the coefficients for a first coordinate of the constellation used in a least squares model for estimating the center of each symbol cluster, and a multiplication circuit which multiplies said inverted first matrix by said third matrix to produce a second coefficient matrix of the coefficients for a second coordinate of the constellation used in said least squares model for estimating the center of each symbol cluster.
- View Dependent Claims (38, 39)
- - 38. The system of claim 37, wherein weighted sum circuit operates to produce said first, second and third matrices, designated A, B_xand B_yin accordance with the following relationships:
    - $A = \sum_{i = 1}^{M} \sum_{j = 1}^{M} \sum_{k = 1}^{K_{ij}} \langle \begin{matrix} 1 & l_{ik} & m_{jk} & l_{ik}^{2} & m_{jk}^{2} & l_{ik}^{3} & m_{jk}^{3} \\ l_{ik} & l_{ik}^{2} & l_{ik} m_{jk} & l_{ik}^{3} & l_{ik} m_{jk}^{2} & l_{ik}^{4} & l_{ik} m_{jk}^{3} \\ m_{jk} & l_{ik} m_{jk} & m_{jk}^{2} & l_{ik}^{2} m_{jk} & m_{jk}^{3} & l_{ik}^{3} m_{jk} & m_{jk}^{4} \\ l_{ik}^{2} & l_{ik}^{3} & l_{ik}^{2} m_{jk} & l_{ik}^{4} & l_{ik}^{2} m_{jk}^{2} & l_{ik}^{5} & l_{ik}^{2} m_{jk}^{3} \\ m_{jk}^{2} & l_{ik} m_{jk}^{2} & m_{jk}^{3} & l_{ik}^{2} m_{jk}^{2} & m_{jk}^{4} & l_{ik}^{3} m_{jk}^{2} & m_{jk}^{5} \\ l_{ik}^{3} & l_{ik}^{4} & l_{ik}^{3} m_{jk} & l_{ik}^{5} & l_{ik}^{3} m_{jk}^{2} & l_{ik}^{6} & l_{ik}^{3} m_{jk}^{3} \\ m_{jk}^{3} & l_{ik} m_{jk}^{3} & m_{jk}^{4} & l_{ik}^{2} m_{jk}^{3} & m_{jk}^{5} & l_{ik}^{3} m_{jk}^{3} & m_{jk}^{6} \end{matrix} \rangle, B_{x =} \sum_{i = 1}^{M} \sum_{j = 1}^{M} \sum_{k = 1}^{K_{ij}} \langle \begin{matrix} x_{ijk} \\ l_{ik} x_{ijk} \\ m_{jk} x_{ijk} \\ l_{ik}^{2} x_{ijk} \\ m_{jk}^{2} x_{ijk} \\ l_{ik}^{3} x_{ijk} \\ m_{jk}^{3} x_{ijk} \end{matrix} \rangle, B_{y} = \sum_{i = 1}^{M} \sum_{j = 1}^{M} \sum_{k = 1}^{K_{ij}} \langle \begin{matrix} y_{ijk} \\ l_{ik} y_{ijk} \\ m_{jk} y_{ijk} \\ l_{ik}^{2} y_{ijk} \\ m_{jk}^{2} y_{ijk} \\ l_{ik}^{3} y_{ijk} \\ m_{jk}^{3} y_{ijk} \end{matrix} \rangle .$
39. The system of claim 38, wherein said first and second coordinate coefficient matrices are of the form:

40. A system for adaptively compensating a digital signal which is being transmitted by a transmitter and received by a receiver, comprising:
- a signal modulator which modulates a digital signal at the transmitter according to a predetermined modulation scheme;
  
  an adaptive compensation circuit which compensates said modulated signal at said transmitter in accordance with compensation values determined from statistical information accumulated at the receiver regarding the received signal;
  
  a transmitter for transmitting said compensated modulated signal to said receiver;
  
  a receiving circuit which receives said compensated modulated signal at said receiver;
  
  a statistical accumulation circuit which accumulates statistical information at said receiver regarding said received signal, said statistical accumulation circuit comprising a symbol cluster accumulation circuit which accumulates symbol cluster statistical information and uses said symbol cluster statistical information to accumulate constellation statistical information, a weighted sum circuit which accumulates weighted sums of the symbol coordinates to produce first, second and third matrices;
  
  an inversion circuit which inverts said first matrix and multiplies said inverted first matrix by said second matrix to produce a first coefficient matrix of the coefficients for a first coordinate of the constellation used in a least squares model for estimating the center of each symbol cluster;
  
  a multiplication circuit which multiplies said inverted first matrix by said third matrix to produce a second coefficient matrix of the coefficients for a second coordinate of the constellation used in said least squares model for estimating the center of each symbol cluster;
  
  a processing circuit which processes said statistical information to determine compensation values for constellation distortions due to at least one of voltage offset, gain mismatch ratio, lock angle error, quad angle error, nonlinear channel distortions and receiver distortions;
  
  wherein said adaptive compensation circuit compensates for said constellation distortions in at least one of the in-phase and quadrature signal components of said signal.
- View Dependent Claims (41, 42, 43, 44)
- - 41. The system of claim 40, wherein said receiver transmits said statistical information over a reverse control channel to said transmitter and said processing circuit is located at said transmitter.
  - 42. The system of claim 40, wherein said processing circuit is located at said receiver and said receiver transmits said compensation values to said transmitter over a reverse control channel.
  - 43. The system of claim 40, further comprising a memory-based predistorter for predistorting said modulated signal prior to transmission.
  - 44. The system of claim 40, wherein said digital signal is part of a signal constellation, and said system further comprises a partitioning circuit which partitions said signal constellation into a plurality of sub-constellations which are processed by said accumulation and processing circuits for the signals within each sub-constellation.

45. A system for adaptively compensating a digital signal which is being transmitted by a transmitter and received by a receiver, comprising:
- a signal modulator which modulates a digital signal at the transmitter according to a predetermined modulation scheme;
  
  an adaptive compensation circuit which adaptively compensates said modulated signal at said receiver in accordance with compensation values determined from statistical information accumulated at the receiver regarding the received signal;
  
  a transmitter for transmitting said modulated signal to said receiver;
  
  a receiving circuit which receives said modulated signal at said receiver;
  
  a statistical accumulation circuit which accumulates statistical information at said receiver regarding said received signal, said statistical accumulation circuit comprising;
  
  a symbol cluster accumulation circuit which accumulates symbol cluster statistical information and uses said symbol cluster statistical information to accumulate constellation statistical information, a weighted sum circuit which accumulates weighted sums of the symbol coordinates to produce first, second and third matrices;
  
  an inversion circuit which inverts said first matrix and multiplying said inverted first matrix by said second matrix to produce a first coefficient matrix of the coefficients for a first coordinate of the constellation used in a least squares model for estimating the center of each symbol cluster;
  
  a multiplication circuit which multiplies said inverted first matrix by said third matrix to produce a second coefficient matrix of the coefficients for a second coordinate of the constellation used in said least squares model for estimating the center of each symbol cluster;
  
  a processing circuit which processes said statistical information to determine compensation values for constellation distortions due to at least one of voltage offset, gain mismatch ratio, lock angle error, quad angle error, nonlinear channel distortions and receiver distortions;
  
  wherein said adaptive compensation circuit compensates for said constellation distortions in at least one of the in-phase and quadrature signal components of said signal.
- View Dependent Claims (46, 47, 48, 49)
- - 46. The system of claim 45, wherein said receiver transmits said statistical information over a reverse control channel to said transmitter, said processing circuit is located at said transmitter and said transmitter transmits compensation values to said receiver over a forward control channel.
  - 47. The system of claim 45, wherein said processing circuit is located at said receiver.
  - 48. The system of claim 45, further comprising a memory-based predistorter for predistoring said modulated signal prior to transmission.
  - 49. The system of claim 45, wherein said digital signal is part of a signal constellation, and said system further comprises a partitioning circuit which partitions said signal constellation into a plurality of sub-constellations which are processed by said accumulation and processing circuits for the signals within each sub-constellation.

50. A method for adaptively compensating a digital signal, comprising the following steps:
- accumulating statistical information at a receiver regarding a received signal transmitted by a transmitter, said accumulating step comprising the further steps of accumulating symbol cluster statistical information, using said symbol cluster statistical information to accumulate constellation statistical information, accumulating weighted sums of the symbol coordinates to produce first, second and third matrices, inverting said first matrix and multiplying said inverted first matrix by said second matrix to produce a first coefficient matrix of the coefficients for a first coordinate of the constellation used in a least squares model for estimating the center of each symbol cluster, multiplying said inverted first matrix by said third matrix to produce a second coefficient matrix of the coefficients for a second coordinate of the constellation used in said least squares model for estimating the center of each symbol cluster;
  
  processing said statistical information to determine compensation values; and
  
  using said compensation values to compensate said signal.
- View Dependent Claims (51, 52, 53, 54)
- - 51. The method of claim 50, wherein said digital signal includes at least one QAM (quadrature amplitude modulation), TCM (trellis coded modulation), CAP (carrierless AM/PM), MPSK (multiple phase shifting keying), QPR (quadrature partial response) and signal constellations.
  - 52. The method of claim 50, wherein said step of accumulating constellation statistical information and said processing step are used to determine predistortion parameters, said method comprising the further step of using said predistortion parameters to predistort said signal prior to transmission of said signal, whereby said received signal symbol clusters are properly located in accordance with predetermined signal decision boundaries.
  - 53. The method of claim 50, further comprising the following steps:
54. The method of claim 50, further comprising the following steps:
- using a memory-based predistorter to compensate said signal;
  
  determining any residual nonlinear distortion still present in said signal; and
  
  if so, adaptively predistorting said signal to substantially eliminate said residual nonlinear distortion.

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Current Assignee
General Dynamics Government Systems Corporation (General Dynamics Corporation)
Original Assignee
General Dynamics Government Systems Corporation (General Dynamics Corporation)
Inventors
Salinger, Sheldon N.
Primary Examiner(s)
Vo, Don N.

Application Number

US08/997,858
Time in Patent Office

1,280 Days
Field of Search

375/261, 375/278, 375/284, 375/285, 375/296, 375/297, 455/63, 455/126
US Class Current

375/278
CPC Class Codes

H03F 1/3247   using feedback acting on pr...

H03F 1/3282   Acting on the phase and the...

H04L 2027/0016   Stabilisation of local osci...

H04L 27/34   Amplitude- and phase-modula...

Adaptive predistortion system

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